Chitosan (CS), also called 2-amino-2-deoxy-β-D-glucose, was the deacetyl chitin (2-acetylamino-2-deoxy-β-D-glucose). Chitin, also called crab shell element, chellotin, chitinous substance, tunicin, etc., is a natural linear polysaccharide and is a primary component of the exoskeletons of crustaceans, which also exists in cell walls of lower plants such as fungi and alga. Since the chitosan contains non toxic, and has good biocompatibility and biodegradability, it has been widely used in the field of medical auxiliary material. The chitosan can form hydrogen bond and electrostatic interaction with the mucosal membrane protein, and has good bioadhesive properties, but the adhesion ability based on the non covalent bond does not guarantee the sustained release of drugs at the targeted part, which limits the application of the chitosan. However, after thiolation of chitosan, the adhesion ability of chitosan is significantly enhanced. This is because that thiomers can form disulfide bonds with mucosal layers, and generate specific binding with the cysteine-rich subdomains of the mucoproteins.
However, the use of thiolated polymers as hydrophobic drug carriers is not ideal. This is because that the reaction between the thiolated polymers and the hydrophobic drug molecules is very weak, thus it usually causes quick release, unsustainable release and bad encapsulation efficiency of the drug.